Method of refining kyanite or



United States Patent M 3,116,140 METHOD OF REFININ G KYANITE ORE Paul J. Bennett, Worcester, Pa., assignor to Reynolds Metals Company, Richmond, Va., a corporation of Delaware No Drawing. Filed May 4, 1961, Ser. No. 107,660 2 Claims. (Cl. 751) This invention relates to the preparation of ores, and more particularly to removing titanium dioxide from ores preliminary to direct reduction to produce high silicon aluminum alloys.

-It has been known that high silicon aluminum alloys are useful for a number of purposes, particularly casting, and that ores such as clays are available in quantity which can be reduced to high silicon aluminum alloys. Such reduction can readily be accomplished by reaction with carbon in a furnace, with a potentially significant economy as compared to the more conventional electrolytic reduction process. However, most clays which are available in sufficient quantity for this purpose have titanium dioxide in an amorphous form as an impurity, in amounts exceeding 1% by weight. This oxide is difficult to remove, and failure to remove it will result in reducing from the ore a high silicon aluminum alloy containing titanium in an amount exceeding the acceptable limits for most industrial purposes.

There is a particular form of ore known as kyanite which is found as a disseminated mineral in metamorphic rocks, and which is commercially mined for use in making refractory linings for industrial furnaces. The kyanite is conventionally calcined at about 2600 F. before it is used as a furnace lining, so that it will have completed its characteristic thermal expansion (about before it is used as a lining. In this conventional process, no effort is made to remove the content of titanium dioxide, known as rutile, because it does no harm in a furnace lining, even though it is present in an amount exceeding 1%.

The present invention provides an economically refined ore, suit-able for direct reduction to produce a high silicon aluminum alloy with a suitable low titanium dioxide content (not over 0.35% by wt.) by utilizing the differential thermal expansion of the kyanite as compared to that of the rutile in the ors. The rutile occurs principally as separate crystals located along the boundaries of the kyanite crystals or along cleavage planes within the kyanite crystals, and when the kyanite is calcined, the intergranular bonds between the rutile crystals and the kyanite are broken by their different degrees of thermal expansion, so that part of the rutile breaks away at once, and most of the balance is readily separated by grinding or otherwise reducing the size of the kyanite particles until the rutile locked inside is released. The original kyanite ore can be heated first to a temperature of about 2500" F. to about 2700 F., and then ground to release more of the rutile, but it is preferable to calcine the kyanite to such temperature in a rotary kiln until the ore becomes friable, and then to complete the reduction in size of the kyanite particles in an attrition machine. The final separation of the rutile from the kyanite particles can be effected by a suitable method, such as sink and float or in a Humphrey spiral. The fact that the rutile remains relatively hard and tough after the 3,115,140 Patented Dec. 31, 1963 kyanite has become friable through calcining helps the final steps of attrition and separation. The attrition of the kyanite is preferably not continued after the particles reach a size range passing about mesh and held on about mesh, since the rutile occurs principally in this mesh range and it would be unnecessary and undesirable to grind the kyanite any finer. Electrostatic separation is also applicable, because kyanite is non-conductive, whereas rutile is conductive. For the purposes of the invention, oalcination is carried out at a temperature range of about 2500 F. to 2700 F. The only upper limit on the time of oalcination is economic, and the lower limit varies with the temperature of calcination. The time and temperature should be enough to make the kyanite friable, and to complete its thermal expansion. For example, at 2600 F. calcination temperature, onehalf hour in a rotary at that temperature is usually sufficient.

The process of the invention has the further advantage that other impurities are removed with the rutile, particularly particles of iron oxide.

Kyanite is found in rocks which also contain quartz, and before treatment in accordance with the invention the rock is ground to reduce the quartz and kyanite to sand-sized particles, and the kyanite particles are separated by froth flotation or other suitable separation means known in the art. When froth flotation is used, the kyanite is usually ground to about 35 mesh before separation from the quartz.

As an example of the practice of the invention, kyanite particles passing 35 mesh and averaging about 48 mesh were analyzed to contain 38.5% SiO 60.37% A1 0 1.12% Fe O and 0.87% TiO and these particles were calcined in a rotating kiln at 2600 F. for about onehalf hour and were then subjected to attrition by mortar and pestle for one minute, which reduced the particles to a size passing 100 mesh but held on 150 mesh. The kyanite particles were then separated by sink and float means (in methylene iodide) and the separated kyanite particles were then analyzed to contain 37.98% SiO 59.82% A1 0 0.86% Fe O and 0.32% Ti0 When this refined kyanite is subjected to direct reduction with carbon in a furnace, a high silicon aluminum alloy is produced having not more than 1% iron and not more than 0.35% titanium, which is within commercially desirable tolerances for such alloys.

Mesh sizes referred to herein are those of a US. Standard sieves having numbers corresponding to the number of mesh openings per linear inch along each side of the sieve.

While present preferred embodiments of the invention have been described, the invention is not limited thereto but may be otherwise variously embodied and practiced Within the scope of the following claims.

I claim:

1. The method of refining an ore comprising kyanite containing about 1% or more by weight of rutile, which ore is combined with a quartz containing material, said method comprising first comminuting the combined substances to particles of approximately sand size (around 35 mesh), separating the kyanite-rutile ore from the quartz containing material, further comminuting the ore so separated to a particle size of about 100 to 150 mesh, heating the further comminuted ore to a temperature 4 Within the range of about 250 0 to 2700 F. to cause differential expansion and cleavage of the rutile from the kyanite, and thereafter recovering said kyanite with a rutile content of not more than about 0.35% by weight.

References Cited in the file of this patent UNITED STATES PATENTS H'ammarberg July 12, 1938 Riveroll Mar. 25, 1947 

1. THE METHOD OF REFINING AN ORE COMPRISING KYANITE CONTAINING ABOUT 1% OR MORE BY WEIGHT OF RUTILE, WHICH ORE IS COMBINED WITH A QUARTZ CONTAINING MATERIAL, SAID METHOD COMPRISING FIRST COMMINUTING THE COMBINED SUBSTANCES TO PARTICLES OF APPROXIMATELY SAND SIZE (AROUND 35 MESH), SEPARATING THE KYANITE-RUTILE ORE FROM THE QUARTZ CONTAINING MATERIAL, FURTHER COMMINUTING THE ORE SO SEPERATED TO A PARTICLE SIZE OF ABOUT 100 TO 150 MESH, HEATING THE FURTHER COMMINUTED ORE TO A TEMPERATURE WITHIN THE RANGE OF ABOUT 2500 TO 2700*F. FOR A TIME PERIOD SUFFICIENT TO CAUSE DIFFERENTIAL THERMAL EXPANSION AND CLEAVAGE OF THE RUTILE FROM THE KYANITE, AND THEREAFTER RECOVERING SAID KYANITE WITH A RUTILE CONTENT NOT GREATER THAN ABOUT 0.35% BY WEIGHT. 